#include <stdio.h>
#include <conio.h>
#include <alloc.h>

/* structure containing a data part and link part */
struct node
{
    int data ;
    struct node * link ;
} ;

void append ( struct node **, int ) ;
void addatbeg ( struct node **, int ) ;
void addafter ( struct node *, int, int ) ;
void display ( struct node * ) ;
int count ( struct node * ) ;
void delete ( struct node **, int ) ;

void main( )
{
    struct node *p ;
    p = NULL ;  /* empty linked list */


    printf ( "\nNo. of elements in the Linked List = %d", count ( p ) ) ;
    append ( &p, 14 ) ;
    append ( &p, 30 ) ;
    append ( &p, 25 ) ;
    append ( &p, 42 ) ;
    append ( &p, 17 ) ;

    display ( p ) ;

    addatbeg ( &p, 999 ) ;
    addatbeg ( &p, 888 ) ;
    addatbeg ( &p, 777 ) ;

    display ( p ) ;

    addafter ( p, 7, 0 ) ;
    addafter ( p, 2, 1 ) ;
    addafter ( p, 5, 99 ) ;

    display ( p ) ;
    printf ( "\nNo. of elements in the Linked List = %d", count ( p ) ) ;

    delete ( &p, 99 ) ;
    delete ( &p, 1 ) ;
    delete ( &p, 10 ) ;

    display ( p ) ;
    printf ( "\nNo. of elements in the Linked List = %d", count ( p ) ) ;
}

/* adds a node at the end of a linked list */
void append ( struct node **q, int num )
{
    struct node *temp, *r ;

    if ( *q == NULL ) /* if the list is empty, create first node */

    {
        temp = malloc ( sizeof ( struct node ) ) ;
        temp -> data = num ;
        temp -> link = NULL ;
        *q = temp ;
    }
    else
    {
        temp = *q ;

        /* go to last node */
while ( temp -> link != NULL )
            temp = temp -> link ;

        /* add node at the end */

        r = malloc ( sizeof ( struct node ) ) ;
        r -> data = num ;
        r -> link = NULL ;
        temp -> link = r ;
    }
}

/* adds a new node at the beginning of the linked list */
void addatbeg ( struct node **q, int num )
{
    struct node *temp ;

    /* add new node */

    temp = malloc ( sizeof ( struct node ) ) ;

    temp -> data = num ;
    temp -> link = *q ;
    *q = temp ;
}

/* adds a new node after the specified number of nodes */
void addafter ( struct node *q, int loc, int num )
{
    struct node *temp, *r ;
    int i ;

    temp = q ;
    /* skip to desired portion */
for ( i = 0 ; i < loc ; i++ )
    {
        temp = temp -> link ;

        /* if end of linked list is encountered */
if ( temp == NULL )
        {
            printf ( "\nThere are less than %d elements in list", loc ) ;
            return ;
        }
    }

    /* insert new node */

    r = malloc ( sizeof ( struct node ) ) ;
    r -> data = num ;
    r -> link = temp -> link ;
    temp -> link = r ;
}

/* displays the contents of the linked list */
void display ( struct node *q )
{
    printf ( "\n" ) ;

    /* traverse the entire linked list */
while ( q != NULL )
    {
        printf ( "%d ", q -> data ) ;
        q = q -> link ;
    }
}

/* counts the number of nodes present in the linked list */
int count ( struct node * q )
{
    int c = 0 ;

    /* traverse the entire linked list */
while ( q != NULL )
    {
        q = q -> link ;
        c++ ;
    }

    return c ;
}

/* deletes the specified node from the linked list */
void delete ( struct node **q, int num )
{
    struct node *old, *temp ;

    temp = *q ;

    while ( temp != NULL )
    {
        if ( temp -> data == num )
        {
            /* if node to be deleted is the first node in the linked list */
if ( temp == *q )
                *q = temp -> link ;

            /* deletes the intermediate nodes in the linked list */
else
                old -> link = temp -> link ;

            /* free the memory occupied by the node */

            free ( temp ) ;
            return ;
        }

        /* traverse the linked list till the last node is reached */
else
        {
            old = temp ;  /* old points to the previous node */

            temp = temp -> link ;  /* go to the next node */

         }
    }

    printf ( "\nElement %d not found", num ) ;
}